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    <title>ShellCheck: SC3025 – In POSIX sh, `/dev/{tcp,udp}` is undefined.</title>
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    <h1>SC3025 – ShellCheck Wiki</h1>
    <a href="https://github.com/koalaman/shellcheck/wiki/SC3025">See this page on GitHub</a>
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    <h2 id="in-posix-sh-devtcpudp-is-undefined">In POSIX sh,
<code>/dev/{tcp,udp}</code> is undefined.</h2>
<p>(or "In dash, ... is not supported." when using
<code>dash</code>)</p>
<h3 id="problematic-code">Problematic code:</h3>
<div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="SC3025.html#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> foo <span class="op">&gt;</span> /dev/tcp/myhost/1234</span></code></pre></div>
<h3 id="correct-code">Correct code:</h3>
<p>Rewrite using a tool like netcat (<code>nc</code>):</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="SC3025.html#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> foo <span class="kw">|</span> <span class="ex">nc</span> myhost 1234</span></code></pre></div>
<h3 id="rationale">Rationale:</h3>
<p><code>/dev/tcp/$host/$port</code> and
<code>/dev/udp/$host/$port</code> are recognized in redirections by bash
and ksh, and a socket connection is made instead of opening a file. They
do not physically exist in <code>/dev</code>.</p>
<p>POSIX sh and dash do not support this, so any such code should be
rewritten to use a socket tool explicitly. The obvious candidate is
netcat aka <code>nc</code>.</p>
<h3 id="exceptions">Exceptions:</h3>
<p>None</p>
<h3 id="related-resources">Related resources:</h3>
<ul>
<li>Help by adding links to BashFAQ, StackOverflow, man pages, POSIX,
etc!</li>
</ul>
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